Recently, a screen is shared between a screen transmitter device operated by a worker and a screen receiver device operated by an instructor by using public line network, such as Internet network. In such a screen sharing, a screen transmitter device and an screen receiver device share a screen displaying an image of a working area taken by a worker, and an instructor inspects the image and conveys a work instruction by voice through a telephone call etc.
For instance, Patent Document 1 discloses a configuration that information is shared through the Internet by transferring images and voices, and the voice data transmitted from other site is output as a voice to a terminal used in a site.